1. Technical Field of the Invention
This invention relates generally to communication systems and more particularly to communication devices within such systems.
2. Description of Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), radio frequency identification (RFID), Enhanced Data rates for GSM Evolution (EDGE), General Packet Radio Service (GPRS), WCDMA, LTE (Long Term Evolution), WiMAX (worldwide interoperability for microwave access), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, RFID reader, RFID tag, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system or a particular RF frequency for some systems) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the receiver is coupled to an antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies then. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers data from the filtered signals in accordance with the particular wireless communication standard.
As is also known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
The data modulation stage includes a plurality of functional blocks that are standard specific to convert data into the baseband signals. For instance, many cellular communication standards require speech coding, as such, the data modulation stage includes a speech coding functional block. In general, speech coding models digital speech signals by using audio signal processing and speech parameter estimations. The speech parameter estimations are based on the known psychoacoustics of the human auditory system such that the intelligibility of the speech is preserved. One specific criteria for speech coding is that it should have low coding delays since long coding delays would interfere with the intelligibility of a cellular communication.
Code excited linear predication (CELP) is a commonly used speech coding scheme in cellular communications. CELP has four main components: linear prediction, codebooks, searching, and quantization. The codebooks, which may be adaptive and/or fixed, contain a plurality of modeled sound samples. A linear prediction model utilizes inputs from the codebooks to make estimations of speech signals, which may be done by performing a closed loop search in a perceptually weighted domain. A vector quantization function is applied to the resulting estimations to produce the coded speech.
While speech coding works well to compress data and generally improve the performance of a cellular communication devices, there are some issues. For example, when a cellular communication device is used in a noisy environment, its audio input circuitry (e.g., microphone and audio coded) receives and captures analog voice signals and the background noise. As such, the resulting digital speech signals include a voice component and a noise component. In this instance, the “noisy” digital speech signals are speech encoded and the noise is passed along with the desired voice signals. A “noisy” encoded digital speech signal can adversely affect the usefulness of a cellular communication device.
Therefore, a need exists for a communication device that has reduced noise speech coding.